Motorized reduction gear unit comprising a hollow casing having a cover plate, especially for a screen wiping apparatus

ABSTRACT

A motorized reduction gear unit having a crank and connecting rod mechanism incorporated in it, but especially for use as a vehicle screen wiper drive unit, comprises a hollow casing having a cover plate, with, within the hollow interior of the casing, a toothed wheel which is rotatable about an axis. The toothed wheel carries a gudgeon pin parallel to the axis of rotation of the toothed wheel but eccentric with respect to the latter. The pin drives a crank and connecting rod system in which the crank and connecting rod are articulated together about a pivot pin, so that continuous rotary motion of the toothed wheel is converted into alternating rotary motion of an output shaft. It further includes a peripheral gasket disposed between the upper edge of the casing and the cover plate, together with a friction plate element in the form of a thickened friction portion disposed fixedly on the inner surface of the cover plate facing towards the casing. The peripheral gasket and the friction plate element together constitute a monobloc component.

This is a continuation of application Ser. No. 08/461,266, filed Jun. 5,1995, now U.S. Pat. No. 5,768,941.

FIELD OF THE INVENTION

This invention relates to a motorised reduction gear unit comprising ahollow casing having a cover plate, especially a motorised reductiongear unit of a screen wiping system for a vehicle.

BACKGROUND OF THE INVENTION

Such a unit generally comprises an electric drive motor together with aspeed reducing mechanism, in particular a mechanism of the worm typeenclosed within the hollow casing by the cover plate.

The casing includes within its hollow interior, as is well known, atoothed wheel which is driven in rotation by the worm, and whichactuates, via an eccentric gudgeon pin carried by this toothed wheel, acrank and connecting rod system which operates an output shaft, in sucha way that the latter moves in alternating rotary motion. The outputshaft extends through the base of the casing for connection with thescreen wiper to be driven by it.

The crank and connecting rod system consists of an arm which isconnected at one of its ends to the eccentric gudgeon pin carried by thetoothed wheel. At its other end, this arm has a toothed sector whichmeshes with a second toothed sector. This second toothed sector is inturn fixed to the output shaft. In order that the two toothed sectorswill remain in continuous engagement, they are linked together on eitherside by means of balance members, which also constitute the crank of thecrank and connecting rod system.

However, such a motorised reduction gear unit has to be able to transmitvery large forces. The crank and connecting rod system is subjected notonly to forces transmitted by the toothed wheel in the axis of rotationof the connecting rod, which can cause the crank and connecting rodsystem stall, so as to give rise to axial displacement of the pivot ofthat system, but also to axial forces on the axis of the gudgeon pin, oron the axis of the output shaft itself.

It has previously been proposed, in a previous patent application of thepresent Applicants, namely French published patent application FR 2 667670A, to immobilise against axial movement the eccentric gudgeon pinwhich is carried by the toothed wheel, by locating it against the coverplate by means of a friction plate which is fixed against the innersurface of the cover plate, and on which the end of the gudgeon pinengages. The same document also proposes the provision of a frictionring surrounding the end of the output shaft and disposed against theinner surface of the cover plate, being in engagement on one of thebalance members that surround the output shaft.

These expedients avoid the situation in which the eccentric pin or theoutput shaft impact on the inner surface of the cover plate accidentallydue to axial forces, so giving rise to noise. However, this problemstill remains in connection with the crank and connecting rod system.

Accordingly, a simple and inexpensive way is sought to improve theoperation of the pivotal connections at the eccentric gudgeon pin of thetoothed wheel, and in the crank and connecting rod system.

In addition, in order to provide sealing against ingress of grease anddust into the flat joint between the cover plate and the casing, it isusual to arrange a gasket between the edge of the said cover plate andthat of the casing. However, this gasket, which is currently made in avery fragile material, is a component which can easily become tornduring assembly operations. In addition, because this component is verymalleable, it is quite a delicate operation to fit it in place in thejoint between the casing and the cover plate.

DISCUSSION OF THE INVENTION

According to the invention, a motorised reduction gear unit comprising ahollow casing having a cover plate, in particular a motorised gear unitfor a screen wiping system, comprising, within the hollow interior ofthe said casing, a toothed wheel which is rotatable about an axis, thetoothed wheel carrying a gudgeon pin having an axis parallel to the saidaxis of the toothed wheel and eccentric with respect to the latter, thesaid pin driving a crank and connecting rod system which is articulatedabout a pivot, whereby to derive from continuous rotational motion ofthe said toothed wheel an alternating rotary motion of an output shaftconnected to the end of the crank, further includes a peripheral gasketportion disposed between the upper edge of the casing and the coverplate, and a thickened friction portion disposed on and fixed withrespect to the internal face of the cover plate facing towards thecasing. It is characterised in that the peripheral gasket portion andthe friction plate constitute a monobloc component.

Thus, by virtue of the invention, the gasket is incorporated in amonobloc component which is in consequence much more rigid than previousarrangements; and handling of this component and its fitting in thejoint between the casing and the cover plate is made much easier.

According to another preferred feature of the invention, the saidmonobloc component comprises, disposed on the internal surface of thecover plate facing towards the casing, an engagement surface forabutting engagement of the crank in the vicinity of the pivot pin.

This solution has the further advantage that the functions of sealing,preventing the ingress of grease or dust into the interior of thecasing, and abutting engagement of the eccentric gudgeon pin carried bythe toothed wheel and of the crank and connecting rod system at itspivot, are all achieved by a single component. In this way, the meshbetween the toothed sectors, and the pivoting couplings on the eccentricgudgeon pin axis and between the connecting rod and crank, are allimproved, so reducing noise occurring at these locations and increasingthe useful life of the various components of the motorised reductiongear unit.

According to another preferred feature of the invention, the saidengagement surface comprises at least one arcuate track arrangedconcentrically with the output shaft.

According to a further preferred feature of the invention, theengagement surface comprises two concentric tracks defining a slot on anarc of a circle.

According to yet another preferred feature of the invention, the circleof which the said arc is a part is centred on the axis of the outputshaft, and has a radius which is substantially equal to the distanceseparating the said axis of the output shaft from the axis of the pivotbetween the crank and the connecting rod.

Thanks to the features mentioned above, the engagement surface providedby the invention is disposed over the whole path of the pivot betweenthe crank and the connecting rod as it rotates about the output shaft.

According to another preferred feature of the invention, the frictionplate portion of the monobloc component is disposed over the wholecircular path of the pin, about the axis of the toothed wheel.

According to a further preferred feature of the invention, the monobloccomponent further includes a perforated friction ring portion arrangedcoaxially with the output shaft. This ring portion provides an abuttingengagement for the output shaft, by immobilising the latter againstaxial movement and against any radial movements of the end of the outputshaft.

According to yet another preferred feature of the invention, the variouselements comprising the gasket and/or thickened friction portion, and/orfriction ring portion and/or engagement surface, of the monobloccomponent, are joined together by connecting means which are moulded inthe monobloc component together with the different elements of the saidcomponent.

According to another preferred feature of the invention, the monobloccomponent is of a material having a low coefficient of friction.

Further features and advantages of the invention will appear moreclearly on a reading of the description of a preferred embodiment of theinvention which follows, and which is given by way of example only andwith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view in cross section showing a motorisedreduction gear unit having a cover plate in accordance with theinvention.

FIG. 2 is a view in elevation of a motorised reduction gear unit showingthe contacts, concentric with the output shaft, attached under the coverplate, the cover plate being considered, for convenience, to betransparent here.

FIG. 3 is a view in elevation of the component in accordance with theinvention, referred to as an abutment gasket, into which the concentricabutting engagement surfaces are incorporated.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

FIGS. 1 and 2 show a motorised reduction gear unit, in particular fordriving a screen wiping system. The unit comprises an electric motor 1and a hollow casing 2 having a cover plate 3. The casing 2 contains areduction gear system which comprises a toothed wheel 4. The wheel 4 isrotatable about a shaft 5, and is driven by means of a worm 6 carried bythe rotor of the electric motor 1. The toothed wheel 4 carries a gudgeonpin 7, which is parallel to the shaft 5 and which is substantiallyoffset eccentrically with respect to the latter. The pin 5 is mountedfor free rotation in a recess 8 formed in the toothed wheel 4.

The pin 7 is coupled to a crank and connecting rod system 9, whichconverts the rotary motion of the toothed wheel 4 into oscillatingmotion, i.e. alternating rotary motion, of an output shaft 10. Theoutput shaft 10 is mounted within a sleeve 11 situated at the base ofthe casing 2 and resting on a bearing 12. Its lower end (not shown)projects out of the casing and is coupled in the usual way to the screenwipers.

The crank and connecting rod system 9 comprises an arm 13, whichconstitutes a connecting rod and is coupled at one of its ends, 14, tothe gudgeon pin 7, in such a way as to leave an end portion 16 of thepin 7 projecting beyond the outer face 15 of the arm 13. The other endof the arm 13 is formed with a toothed sector 17. This toothed sectormeshes at 19 with another toothed sector 18, which is fixed to theoutput shaft 10.

The two toothed sectors 17 and 18 are held in constant engagement bymeans of two balance members 20a and 20b, which are located on eitherside of the longitudinally extending faces of the toothed sectors 17 and18. The two balance members 20a and 20b constitute the crank of thesystem mentioned above, coupling the arm 13 and the output shaft 10rigidly together. The two balance members are held together, firstly bymeans of an aperture 22a (for the balance member 20a) and an aperture22b (for the balance member 20b ), these apertures being arranged at oneend of the balance members and surrounding an end portion 23 of theoutput shaft 10. The balance members are also held together by a freelyrotatable pivot pin 21 which is disposed at the other end of the balancemembers. In this way, the two balance members 20a and 20b are able torotate about the output shaft 10. The pivot pin 21 is the pivot of thecrank and connecting rod system.

In a modification which is not shown in the drawings, the crank andconnecting rod system consists of a first arm which is coupled at one ofits ends to the gudgeon pin carried by the toothed wheel, while at itsother end this arm is connected to a second arm, or crank, through apivot pin, this second arm being itself connected to the output shaft.

As can best be seen in FIG. 1, the pivot pin 21 has two differentdiameters, namely a first diameter in its central part, substantiallysmaller than the diameter of the bore 25 of the arm 13 so that the pivotpin can be inserted with minimal clearance into the arm 13; and a seconddiameter occurring at its two ends. This second diameter issubstantially smaller than the diameter of the bores 24a and 24b in thetwo balance members 20a and 20b.

With reference to FIG. 1, the pivot pin 21 has an axial length which isgreater than the combined thickness of the two balance members 20a and20b and the arm 13, so as to leave free two end portions 26a and 26bwhich project on either side of the balance members. These end portions26a and 26b are upset so as to form two rivet heads, which are alsodesignated by the reference numerals 26a and 26b. These rivet headsretain the two balance members 20a and 20b axially about the arm 13.

Still with reference to FIG. 1, the cover plate 3 closes off the top ofthe casing 2. The cover plate 3 is formed generally from a thin metallicsheet, and is connected to the edges of the casing in any known way, forexample by means of screws or riveting. On its inner face, the coverplate is provided with a friction plate element in the form of athickened portion 27a, 27b. This plate element, which is fixed withrespect to the cover plate, surrounds the rivet head 26a and defines twocontact tracks 37a and 37b, which can be seen in FIG. 2 and which areconcentric with the output shaft 10.

In this example, the thickened portion 27a, 27b is of a plasticsmaterial having a low coefficient of friction, and is a separate elementattached flat on the cover plate 3.

It is also arranged that the concentric contact tracks 37a and 37b areof such a thickness that the thickened portion 27a and 27b is incontact, or abutting engagement, with the upper surface of the balancemember 20a. This can best be seen in FIG. 1.

The concentric tracks 37a and 37b define between them a guide slot inthe form of an arc of a circle. The composition and form of this arcuateguide slot 37a, 37b, are such that the rivet head 27a, projecting fromthe surface of the balance member 27a, is able to slide within the guideslot. For this reason, the radius R of the circle of which the arcdefined by the guide slot 37a, 37b forms a part, corresponds to thedistance between the axis 29 of the output shaft 10 and the axis 28 ofthe pivot pin 21.

In this way, the balance members 20a, 20b are guided in their rotationalmovement about the shaft 10 by the rivet head 26a sliding between theconcentric contact tracks 37a and 37b. In addition, the contact of thethickened portion 27a, 27b with the balance members 20a, 20b avoidsstalling of the balance members, when the arm 13 constituting aconnecting rod transmits the rotary motion to the crank constituted bythe balance members. The concentric contact tracks 37a and 37b thuseliminate axial forces due for example to a poor working position,which, added to the radial forces prevailing, are detrimental to thecoupling between the pivot pin 21 and the arm 13 that constitutes aconnecting rod.

In addition, the two end portions 30a and 30b of the arcuate guide slot37a, 37b are able to act as end stop abutments for the upset rivet head26a, so as to limit shocks occurring at the instant of reversal of themeshing engagement.

In the example shown in FIG. 1, the inner face of the cover plate 3 has,in addition to the thickened portion 27a, 27b, two further thickenedportions 31 and 32. These further thickened portions are an integralpart of a component 40 which includes a gasket portion 33 laid betweenthe edge of the casing 2 and the edge of the cover plate 3.

The component 40 will be referred to as an abutment gasket. One form ofthis component is shown in FIG. 3, to which reference is now made. Itcomprises the gasket portion 33 at the periphery of the abutment gasket40, together with a flat, circular plate portion 41, a ring portion 42,and the contact tracks 37a, 37b defining the arcuate guide slot. Theabutment gasket 40 is made of a material having a low coefficient offriction, and it is arranged that it can be positioned in engagementagainst the cover plate 3, with the gasket portion 33 lying between theupper edge 50 of the casing 2 and the edge 51 of the cover plate 3, ascan best be seen in FIG. 1.

The form of the gasket portion 33 is reproduced on the upper edge 50 ofthe casing 2 (with reference to FIG. 2), and on holes 52a to 52f formedin the upper edge 50, which correspond to holes 53a to 53f in the gasketportion 33. These holes 53 can be seen in FIG. 3, and the holes 52 and53 enable the casing 2 and the cover plate 3 to be fixed together, bymeans of screws or rivets for example.

The gasket portion 33 thus slides exactly at the junction between thecover plate 3 and the casing 2, and provides sealing between these twocomponents. In this connection it prevents grease or dust frompenetrating into the casing.

Referring to FIG. 3, the flat plate portion 41 has a circular periphery,the radius R' of which is at least equal to the radius r measuredbetween the axis of the shaft 5, i.e. the axis of rotation of thetoothed wheel 4, and the axis of the gudgeon pin 7 which can be seen inFIG. 2. The radius R' is preferably equal to the radius r increased bythat of the pin 7. The plate portion 41 is coaxial with the shaft 5, andengages against the cover plate 3.

Thus, during fitting and screw fastening of the cover plate 3 on theedge 50 of the casing, the outer face 54 of the plate portion 41, facingtowards the casing 2, lies in sliding relationship on the upper surfacelocated at the end 16 of the pin 7. Because of the composition and thecircular form of the plate portion 41, the terminal surface of the endportion 16 of the pin 7 is able to slide easily throughout the circularmotion of the pin 7 about the shaft 5, while the pin 7, and thereforealso the end portion 14 of the arm 13 constituting the connecting rod,is positively located in the axial direction.

Still with reference to FIG. 3, the perforated ring portion 42 of theabutment gasket 40 has a central hole 55, the diameter of which issubstantially greater than the diameter of the end portion 23 of theoutput shaft 10. It is arranged coaxially with the axis 29 of the outputshaft 10, so as to surround the end portion 23; it engages firstly onthe balance member 20a and secondly on the cover plate 3, when thelatter is fitted on to the casing 2, as can best be seen in FIG. 1. Aspace is of course provided between the terminal surface 6 of the endportion 23 of the output shaft 10 and the inner surface of the coverplate 3, i.e. the surface facing towards the interior of the casing 2,when the cover plate is fitted on to the casing. The thickened portion32 will be arranged to have a thickness sufficient to allow the endportion 23 of the output shaft 10 to avoid making contact with the innerface of the cover plate 3.

Thus, the output shaft 10 is held against axial movement by thethickened portion 32, and in addition, any radial movement of theportion of the output shaft 10 lying beyond the bearing 12 is preventedby the fact that its end portion 23 is disposed within the hole 55 ofthe ring portion 42. Thus the hole 55 acts in this case as a radialbearing.

The abutment gasket 40 thus provides a single component which has all ofthe following functions:

sealing against ingress of grease and dust into the joint between thecasing 2 and the cover plate 3, by virtue of the gasket portion 33;

axial abutting engagement and radial retention at the upper end of theoutput shaft 10, by virtue of the ring portion 42;

abutting frictional engagement of the gudgeon pin 7, at the end of thearm 13 constituting the connecting rod coupled to the toothed wheel 4,by virtue of the plate portion 41; and

engagement and guiding for the ends of the balance member that definesthe crank, so as to avoid the latter becoming stalled, this being due tothe arcuate guide slot 37a, 37b.

The various connections, such as the connection between the pivot pin 21and the connecting rod arm 13, the connection between the gudgeon pin 7and the toothed wheel 4, and the connection between the shaft 5 carryingthe toothed wheel 4 and the latter, are all improved, as is the meshingengagement between the toothed sectors 17 and 18.

In practice, and as can be seen in FIG. 3, the arcuate guide slot 37a,37b is connected to the gasket portion 33 through tongues 44a and 44b.The plate portion 41 is connected to the gasket portion 33 through a setof tongues 42a to 42e, while the ring portion 42 is connected to thegasket portion 33 by means of tongues 43a to 43c. In addition, thearcuate guide slot 37a, 37b is connected to the plate portion 41 at ajunction 57, while an arm 45 joins the ring portion 42 and plate portion41 together. In this way, the abutment gasket 40 is a monobloccomponent, which can for example be made by moulding.

It is of course possible to omit connecting together in one piece thefollowing elements: the guide slot 37a, 37b, the plate portion 41, thering portion 42 and the gasket portion 33. This can for example beachieved by fixing one or more of these elements directly on to theinner face of the cover plate 3, by means of pegs or in any othersuitable known way.

In addition, in the case in which the cover plate 3 is made of aplastics material, this material is of a low coefficient of friction, insuch a way as to form, in conjunction with the cover plate, thethickened portions 27a and 27b of the arcuate guide slot 37a, 37b and/orthe thickened portion 31 of the plate portion 41, and/or the thickenedportion 32 of the ring portion 42, by making a single component in thesame material.

In this document, the invention has been described in relation to amotorised reduction gear unit in which the crank mechanism consists ofan arm defining a connecting rod having a toothed sector meshing inanother toothed sector. However, it is of course also applicable to anyother type of motor having a crank and connecting rod mechanismincorporated with it.

What is claimed is:
 1. A monobloc abutment gasket for a motorizedreduction gear unit having a plurality of components comprising aperipheral gasket formed of a plastic material that has a lowcoefficient of friction, an abutment surface within said peripheralgasket for engaging at least one component of a reduction gear unit toreduce noise and increase the service life of the component of areduction gear unit, a friction ring portion formed of said lowcoefficient of friction plastic material within said peripheral gaskethaving at least one hole having a center to provide a radial bearing, athickened portion at the periphery of said hole to hold at least anotherone of the components of a gear unit against axial movement, tongues forconnecting said peripheral gasket with said abutment surface formed ofsaid low coefficient of friction plastic material, at least one of saidtongues having an arcuate guide slot formed therein for controlling amovement of at least one of the components of a reduction gear unit, andfurther tongues formed of said low coefficient of friction material forjoining said friction ring portion to said peripheral gasket, whereby asturdy monobloc gasket is provided with an integral abutment surface ina single component for easy installation in a motorized reduction gearunit.
 2. A monobloc abutment gasket according to claim 1 wherein said atleast one of said tongues having an arcuate guide slot further comprisesa separate element attached to the peripheral gasket.
 3. A monoblocabutment gasket according to claim 1 wherein said tongue having saidarcuate guide slot formed therein further comprises contact tracks forsaid guide slot, at least a portion of said contact tracks havingthicknesses essentially equal to said thickened portion at the peripheryof said hole.
 4. A monobloc abutment gasket according to claim 1 whereinsaid arcuate guide slot defines a circular arc of a circle, said holecenter being the center for said circular arc.
 5. A monobloc abutmentgasket according to claim 4 wherein said circular arc of said arcuateguide slot terminates in end portions, said end portions comprisingstops.
 6. A monobloc abutment gasket according to claim 1 wherein saidabutment surface further comprises a flat, circular construction.